Convective heat transfer characteristics of impingement cooling for a self-excited precessing jet

Heat transfer performance under precessing jet impingement cooling was experimentally studied.The flow characteristic of the self-excited precessing jet was firstly investigated by a frequency spectra analysis to the jet velocity obtained at the nozzle exit.It was demonstrated that the precessing frequency of the jet was greatly influenced by the nozzle diameter while the Strouhal number was only slightly influenced by the nozzle diameter and the flow rate.The heat transfer experiments indicate that,because of the considerable decrease of the bulk velocity in a precessing jet caused by the surrounding air entrainment,the convective heat transfer coefficients of a precessing jet impingement decrease as compared to that of the corresponding inline jet.The influence of the nozzle diameter on heat transfer characteristics,however,has no uniform trend for three sized nozzles.It is shown that,only in the case that a precessing jet flows parallelly over a heating plate,the convective heat transfer coefficient is higher than that of an inline jet.